What you think matters.

参考译文：你思考/考虑事情是很重要的。

句子语法结构分析

主语：what you think

谓语：matters

备注：what=the thing that 为复合型连接代词，引导主语从句

matter  vi.有关系;要紧;有影响(英文解释： If you say that something does not matter, you mean that it is not important to you because it does not have an effect on you or on a particular situation.)

A lot of the food goes on the floor but that doesn't matter. 

许多食品掉在地板上，不过也没什么关系。

As for Laura and me, the colour of our skin has never mattered. 

至于我和劳拉，肤色根本不是问题。

    What you think matters.= The thing which you think matters.你考虑的事情很重要。

    【说明】这里的 matters 是动词第三人称单数形式，作谓语。意思是“很重要”。 What you think 是主语从句，which you think 是定语从句。